Should I use POP3 or IMAP?

Simply stating which one you should choose isn’t that easy as it depends on various factor but also your personal preference.

In addition, there are various technical differences and limitations to consider which could also influence your decision.

In short…

Before making things complicated, there is actually a pretty good rule of thumb to go by to quickly make a good decision which fits most common scenarios:

• If you mainly work with your email from 1 computer and online mailbox space is limited, POP3 is the way to go.
• If you frequently use multiple devices to work with your email and/or online mailbox space isn’t directly limiting you, IMAP might be the better choice.

Of course, this is just a guideline and there often good reasons to do otherwise or even access your mailbox with POP3 from one computer and via IMAP on another computer or mobile device (see the “My configuration” section for one such example).

POP3

When you configure your mail account as a POP3 account in Outlook, everything that is in your Inbox folder of your webmail account will be downloaded. It really only supports the Inbox folder, so when you’ve stored your mail into various folders in your webmail account or have items in your Sent Items folder on the web, these won’t be downloaded (but still can be).

POP3 is download only, so changes you make locally, will not be uploaded back to the server nor to any other computer or device. This also includes Sent Items and the Read/Unread status of your messages. If the message was already marked as read on the server, it will be downloaded as Unread in Outlook.

Originally, POP3 accounts directly removed the message from the server when they’ve been collected in Outlook. Starting with Outlook 2010 and continued in Outlook 2013, the default setting is to leave the messages on the server for 14 days after they have been downloaded in Outlook. You can alter this setting in any version of Outlook.

Another major characteristic of POP3 accounts is that, when you have multiple POP3 accounts configured in Outlook, you can set them to download to separate mailboxes (pst-files) in Outlook, to separate folders within a single mailbox or simply deliver everything to the same Inbox folder.

Note that data of POP3 accounts only exists on your local computer. Make sure that you include the pst-file(s) that you have are included in your backups.

IMAP

When you configure your account as an IMAP account in Outlook, everything that is stored in your webmail account will be cached. I say cached, because with an IMAP account, there is an active sync taking place between your data in Outlook and your webmail account. This means that all your folders that exist on webmail now also exist in Outlook.

This sync relation means that any changes that you make in Outlook, will also be uploaded back to the server and thus other computer and devices that you have configured with this IMAP account. This includes your Sent Items, deletions and the Read/Unread status of your messages.

A thing you’ve probably directly noticed is that you now have an extra folder set in Outlook or have some folders marked with “This computer Only” (since Outlook 2013). This is because IMAP only supports synching Mail folders and doesn’t offer support for other folder types such as Calendars and Contacts. For more information about this see:Remove empty Personal Folders list and Don’t risk losing your Contacts and Calendar when using IMAP in Outlook 2013.

Other notable differences, compared to POP3, is that the use of Flags with Reminders and Categories is limited. And you may have to manually configure some folders to keep your Sent Items and Deleted Items folder synched as well (which is even a bit trickier in Outlook 2013).

In addition, deleting items works a bit different as well in IMAP accounts as IMAP doesn’t really have the concept of a Deleted Items folder. Instead of moving items to a Deleted Items folder, messages get “marked for deletion” and need to get “purged”. You’ll recognize these items with a strikethrough. Outlook 2010 and Outlook 2013 purge deleted items automatically upon switching folder and create a copy of the item in the Deleted Items folder.

Note that synching isn’t the same as having a backup. When a message gets deleted on any device, it will also get deleted on the server and any other device as soon as they sync. Backups can be made on the IMAP server or locally via exports. Don’t forget the Calendar, Contacts, Tasks, Notes and Journal folders or the pst-file containing them.

Limitations of both IMAP and POP3

Of course, the biggest limitation is that you can’t sync Calendar and Contacts folders with neither POP3 nor IMAP. If you also want support for this, you’ll need a 3rd party syncing tool such as CodeTwo Outlook Sync or iCloud or (even better) use a mail account type which also support synching these folder types such as an Outlook.com account or an Office 365 (Exchange Online) account.

An Outlook.com account can also be used with your own current email address, even when you don’t have a domain of your own.

My configuration

Before I switched to Office 365 (Exchange Online), I’ve used the following configuration:

• Main computer
  POP3 with the option to leave messages on the server for 31 days.
• Laptop, tablet and smartphone
  IMAP and every month (or when needed) I downloaded the Sent Items of the IMAP account on my main computer.

For me, this worked because I mostly worked on the “main computer” where I wanted to have my full mail archive. When I was “on the road” or simply working on another device, I usually only wanted to keep up with new emails, so only having the last 31 days available wasn’t a big limitation.

This configuration also gave me the benefit of having the Calendar and Contacts folder within the same pst-file and some other features which don’t really play nice with an IMAP account like Categories and Flagging messages for Follow Up as already mentioned in the IMAP section.